Method for collecting hard olefin

Abstract

The present invention relates to a method for recovering light olefins, which can achieve an increase in propylene production and a reduction in the basic unit of a process by feeding steam into five serially connected dehydrogenation reactors, and can diversify the product of a propane dehydrogenation reaction process from a propylene single product into propylene and ethylene by separately collecting ethane and ethylene, i.e., by-products of the propylene production process, and converting the ethane into ethylene, thereby improving the economic efficiency of the process and selectivity.

The invention claimed is: 
     
       1. A method for recovering light olefins, the method comprising:
 subjecting a propane-containing feedstock to a dehydrogenation reaction in five serially connected dehydrogenation reactors, wherein the dehydrogenation reaction is performed by feeding the propane-containing feedstock and hydrogen, preheated by two parallel-connected reaction material heaters, into each of the dehydrogenation reactors, and feeding steam separately into each of the dehydrogenation reactors; 
 cooling and compressing a process stream discharged from the last dehydrogenation reactor; 
 quenching the process stream by passage through an ethylene/propylene freezer so that a hydrogen/propane ratio is 0.4 or less; 
 transferring the quenched process stream into a de-ethanizer in which ethane and ethylene are separated from the process stream; 
 separating a process stream containing propane and propylene, separated from the de-ethanizer, by a propane/propylene splitter, thereby obtaining a propylene product; 
 transferring a process stream rich in ethane and ethylene, separated from the de-ethanizer, into a demethanizer in which methane is separated in advance from the process stream; 
 transferring the process stream, from which the methane has been separated, into an acetylene converter in which acetylene in the process stream is converted into ethane and ethylene; 
 separating the process stream, transferred from the acetylene converter, into ethane and ethylene by passage through an ethane/ethylene splitter, thereby obtaining an ethylene product; and 
 converting the ethane, separated from the ethane/ethylene splitter, into ethylene by an additional reaction in an ethane reactor, thereby obtaining an ethylene product. 
 
     
     
       2. The method of  claim 1 , further comprising:
 cooling the process stream, which has passed through the ethane reactor, by passage through a quenching tower, compressing the cooled process stream by a compressor, neutralizing the compressed process stream by passage through a scrubber; and 
 recycling the neutralized process stream to the dehydrogenation process by introducing the neutralized process stream into a rear end of a main compressor in the propane dehydrogenation process. 
 
     
     
       3. The method of  claim 1 , further comprising:
 after cooling and compressing the process stream discharged from the last dehydrogenation reactor and before passing the process stream through the ethylene/propylene freezer, removing hydrogen chloride and hydrogen sulfide (H 2 S) from the process stream. 
 
     
     
       4. The method of  claim 1 , further comprising:
 after quenching the process stream by passage through the ethylene/propylene freezer, adsorbing and removing carbon monoxide (CO) from a process stream coming out from a cooling box, and then transferring the process stream to a hydrogen purification step. 
 
     
     
       5. The method of  claim 1 , further comprising:
 pretreating the propane feed, and then transferring the pretreated propane feed into a depropanizer in which at least a portion of C4+ hydrocarbons is separated as a bottom stream and a first purified propylene-containing product containing C3 or lighter hydrocarbons and hydrogen is separated as an overhead stream. 
 
     
     
       6. The method of  claim 2 , further comprising:
 drying the process stream, neutralized by neutralizing the compressed process stream, in a dryer unit to remove impurities. 
 
     
     
       7. The method of  claim 6 , further comprising:
 capturing a hydrogen gas separately from the process stream that has passed through the dryer unit; increasing a purity of the hydrogen gas in a pressure swing adsorption (PSA) unit, and 
 recovering the hydrogen gas. 
 
     
     
       8. The method of  claim 1 , further comprising:
 transferring unreacted propane, separated from the propane/propylene splitter, to a front end of the dehydrogenation reactor through a propane recycle pipeline, and recycling the transferred unreacted propane as a feed propane gas. 
 
     
     
       9. The method of  claim 1 , wherein the methane in separating the methane in advance in the demethanizer has a temperature of −20° C. to 80° C. and a pressure of 0.4 kgf/cm 2  to 8 kgf/cm 2 . 
     
     
       10. The method of  claim 1 , wherein a heat unit is disposed in front of the ethane reactor to supply heat necessary for the reaction in the ethane reactor. 
     
     
       11. The method of  claim 1 , wherein process conditions of the ethane reactor are a reaction temperature of 650° C. to 950° C. and a pressure of 0.1 kgf/cm 2  to 10 kgf/cm 2 . 
     
     
       12. The method of  claim 1 , wherein a separate feed gas line is disposed in front of the ethane reactor, and
 wherein the method further comprises: 
 controlling a ratio of ethylene production to propylene production by supplying propane through the feed gas line. 
 
     
     
       13. A method for recovering light olefins, the method comprising:
 subjecting a propane-containing feedstock to a dehydrogenation reaction in serially connected at least two dehydrogenation reactors, wherein the dehydrogenation reaction is performed by feeding the propane-containing feedstock and hydrogen, preheated by parallel-connected reaction material heater(s), into each of the dehydrogenation reactors, and feeding steam separately into each of the dehydrogenation reactors; 
 cooling and compressing a process stream discharged from the last dehydrogenation reactor; 
 quenching the process stream by passage through an ethylene/propylene freezer so that a hydrogen/propane ratio is 0.4 or less; 
 transferring the quenched process stream into a de-ethanizer in which ethane and ethylene are separated from the process stream; 
 separating a process stream containing propane and propylene, separated from the de-ethanizer, by a propane/propylene splitter, thereby obtaining a propylene product; 
 transferring a process stream rich in ethane and ethylene, separated from the de-ethanizer, into a demethanizer in which methane is separated in advance from the process stream; 
 transferring the process stream, from which the methane has been separated, into an acetylene converter in which acetylene in the process stream is converted into ethane and ethylene; 
 separating the process stream, transferred from the acetylene converter, into ethane and ethylene by passage through an ethane/ethylene splitter, thereby obtaining an ethylene product; and 
 converting the ethane, separated from the ethane/ethylene splitter, into ethylene by an additional reaction in an ethane reactor, thereby obtaining an ethylene product.